The military trial of the WikiLeaks suspect Bradley Manning is being conducted amid far more secrecy than even the prosecution of the alleged 9/11 plotters in Guantanamo, a coalition of lawyers and media outlets protest.

Led by the New York-based Center for Constitutional Rights, the coalition has petitioned the Army court of criminal appeals calling for the court-martial against Manning to be opened up to the press and public. The group complains that the way the trial is being handled by the trial judge Colonel Denise Lind is a violation of the First Amendment of the constitution that requires public access unless the government can specifically demonstrate the need for secrecy.

The petition lists the many ways in which the public are being kept in the dark over the prosecution of Bradley Manning, who faces 22 charges related to the leaking of a vast trove of US state secrets to the whistleblower website WikiLeaks. He was arrested in May 2010 at a military base outside Baghdad where he was working as an intelligence analyst on suspicion of passing hundreds of thousands of US diplomatic cables as well as warlogs from Iraq and Afghanistan to the site.

The army has allowed the publication of not one single motion submitted by the prosecution to the court-martial, nor any prosecution replies to defence motions, not even in redacted form. None of the orders issued by the court have been made public, and no transcripts have been provided of any of the proceedings – not even those that were fully open to the press.

The petitioners include Julian Assange, the founder of WikiLeaks, as well as news outlets and individuals such as the Nation, Amy Goodman of Democracy Now! and Salon blogger Glenn Greenwald. They say that the lack of openness is all the more serious given the gravity of the charges and the high-profile nature of the court martial which they liken to the trial of Lt William Calley for the My Lai massacre in Vietnam and the legal tussle over the publication of the Pentagon Papers.

Members of the Bradley Manning support network who have attended each of his pre-trial hearings have castigated the "outrageous obfuscations" of the Obama administration over the trial. "Why has the administration spent two years trying to hide basic facts from the defense, the press and the American people?" said Jeff Paterson, a co-founder of the network.

The only documents that have emerged from the proceedings so far are those that have been published by Manning's defence lawyer, David Coombs, on his blog. Coombs has consistently protested about the lack of transparency in the conduct of the court-martial.

In a new post to his blog, Coombs has published the latest set of defence motions ahead of a pre-trial hearing at Fort Meade military base in Maryland scheduled for 6 June. In one of the motions, Coombs complains that over the past two years Manning has been denied the opportunity to take part in his own defence in any meaningful way. He has had no chance to review some 7,000 documents handed to the defence team by the army because no arrangement has been made to allow him secure access to the files from his location in custody.

The only accessible documents are stored in Rhode Island and Maryland, far from where he is being held in Fort Leavenworth, Kansas.

Another motion that will be put to the June hearing calls on the judge to dismiss many of the most serious charges against Manning on the grounds that the language used in them is unconstitutionally vague. The defence objects to phrases such as "to the injury of the US or to the advantage of any foreign nation" which it says are problematically broad in scope.